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Sahithyan's S3
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Sahithyan's S3 — Data Communication and Networking

Web

Most popular application on the internet. A collection of interconnected documents and other resources. Servers and clients communicate using the HTTP protocol which runs on top of TCP/IP.

HTTP, by default, is stateless; no past information is stored between requests. But HTTP can be made stateful using cookies or other mechanisms on the application level.

URL

Section titled “URL”

Short for Unique Resource Locator. Unique identifier for resources on the web.

Client

Section titled “Client”

Device that is used to access the internet. Device that requests resources from a server.

Server

Section titled “Server”

Device that is used to store and serve resources to clients.

HTTP Message

Section titled “HTTP Message”

Can either be a request or a response. End of message is indicated by a blank line.

Request

Section titled “Request”

Message sent from a client to a server to request a resource.

Example:

GET /index.html HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0
Accept: text/html

Response

Section titled “Response”

Message sent from a server to a client in response to a request.

Example:

HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 1256


<html>
  <head><title>Example</title></head>
  <body>Hello, world!</body>
</html>

Verbs

Section titled “Verbs”

Aka. HTTP methods. Defines the type of action to perform on a resource. The most common verbs are:

  • OPTIONS
    Retrieve information about the communication options available on the server.
  • HEAD
    Retrieve metadata about a resource without downloading it.
  • GET
    Retrieve data from the server.
  • POST
    Send data to the server to create a new resource.
  • PUT
    Update an existing resource on the server.
  • DELETE
    Remove a resource from the server.
  • PATCH
    Partially update an existing resource.

Each verb indicates the intended operation and helps servers understand how to process the request.

Destination URL

Section titled “Destination URL”

HTTP requests specify a destination URL, which is the address of the resource being requested. It can either be an absolute URL or a relative URL. Absolute URLs include the protocol, domain name, optionally the port number, and path. Relative URLs are relative to the current URL.

Port number is an optional part of the URL that specifies the port number on which the server is listening. If not specified, the default port number for the protocol is used. HTTP uses port 80. HTTPS uses port 443.

Version

Section titled “Version”

HTTP requests specify a version number, which indicates the version of the HTTP protocol being used. The most common version is HTTP/1.1, but HTTP/2 and HTTP/3 are also supported.

HTTPS is a secure version of HTTP that uses SSL/TLS encryption to protect data in transit. It is recommended to use HTTPS whenever possible to ensure the security of data in transit.

Headers

Section titled “Headers”

Key-value pairs included in an HTTP message. Provide metadata about the message and can be used to control the behavior of the message. Key and value are separated by a colon.

Some common HTTP headers include:

  • Host
    Specifies the domain name of the server (for virtual hosting).
  • User-Agent
    Identifies the client software making the request.
  • Accept
    Indicates the media types the client can process.
  • Content-Type
    Specifies the media type of the resource or data being sent.
  • Content-Length
    Indicates the size of the message body in bytes.
  • Authorization
    Contains credentials for authenticating the client with the server.
  • Cookie
    Sends stored cookies from the client to the server.
  • Set-Cookie
    Used by the server to send cookies to the client.
  • Cache-Control
    Directs caching behavior for requests and responses.
  • Location
    Used in responses to redirect the client to a different URL.

Status

Section titled “Status”

Included in the response. Indicates the outcome of a request. The most common status codes are:

  • 200 OK
    The request was successful.
  • 301 Moved Permanently
    The resource has moved permanently to a new URL.
  • 400 Bad Request
    The request was malformed or invalid.
  • 404 Not Found
    The requested resource was not found.
  • 500 Internal Server Error
    An error occurred on the server.
  • 503 Service Unavailable
    The server is currently unavailable.
  • 505 HTTP Version Not Supported
    The server does not support the HTTP version used in the request.

Each status code indicates the outcome of a request and helps clients understand how to handle the response.